Air Quality in the Tahoe Basin

10 key questions and answers

Overall, the air in the Lake Tahoe Basin is still much clearer than major urban areas, according to Alan Gertler, vice president of research and chief science officer at the Desert Research Institute. However, because Tahoe is visited by millions of people each year and considered by many as one of the few remaining pristine environments in the West, Gertler knows how critical air quality and visual range are to the future of the basin.

With more than 35 years of air quality research experience at Tahoe and around the world, Gertler shared his expertise to help answer 10 of the most common questions about air quality.

Why should we care about air quality in the Tahoe Basin?When we look around Tahoe, the air usually looks clean, but it is one of the few areas in the region where ozone is increasing. It is now at a point where it will likely violate ambient air quality standards. Research also shows that air is a significant source of pollutants that lead to declining water clarity. If we want to reverse this trend, we need to consider making some atmospheric changes.

What air pollutants should we be concerned about?Both nitrogen and phosphorus lead to algae growth in the lake. We should also consider particulate matter because it, too, can deposit in the lake and reduce the clarity of the lake and its surrounding basin. A hazy day is caused by particulate matter. We’re also concerned about ozone because of the negative effects it has on human health and the ecosystem.

What are the sources of the pollutants?Particulate matter comes from road dust or soil, wood burning and emissions from cars, trucks and boats. Nitrogen is also from cars, trucks and boats, while phosphorus is from the soil and wood burning. Ozone is completely formed by chemical reactions in the atmosphere. The sources that are precursors to ozone formation include the mobile sources and the natural emission of hydrocarbon from trees.

Are these air pollutants from inside or outside the basin?Studies have shown that a large majority of the pollutants come from sources inside the basin, as opposed to being transported from areas such as the Sacramento Valley or Bay Area. Since the wind tends to blow from west to east, the primary sources are also not from other locales in northern Nevada.

Is wood burning a significant source of the pollutants?Clearly, it is. There are three major sources of wood burning: fireplaces, prescribed burns and wildfires. We’re not necessarily able to control wildfires, but we can control fireplaces and prescribed burns. In the future, we need to consider the weather conditions and air quality prior to scheduling prescribed burns. In winter, greater consideration should be given to controlling the use of fireplaces.

How important is road dust as a pollutant?It’s surprisingly important in terms of contributing to the decline in water quality. Large particles kick up and get scattered in the lake, they reduce visibility, and they contain phosphorus from the soil that leads to the growth of algae in the lake.If we look at the two factors that lead to declining water quality, algae growth and sediment deposition, current estimates show that 55 percent of nitrogen and 15 percent of phosphorus that deposit into the lake come from atmospheric sources.

What can we do to control road dust?Much of the dust comes from the sand and salt used on the roads during the winter snows. From a safety standpoint, we need to use it. However, what we could do instead is to increase the use of street sweepers and liquid de-icers, both of which would reduce soil on the road that can be re-suspended.

What role does fire play in air quality?Fires are important from the standpoint of visibility in the basin. We want to be able to see across the lake, and fires greatly reduce the visual range. It’s important the air be as clear as possible for many reasons, including aesthetics, yet there are no federal standards regarding visibility. The Tahoe Regional Planning Agency, however, does have a visibility standard.

What can we do to control sources of pollutants?The most important sources we have to control are boats and the mobile sources, cars and trucks. Those sources provide the precursors to forming ozone, and they are also a significant source of particulate pollution.

How were the sources of the pollutants determined?Two types of studies were conducted to determine the most important sources of pollutants: a bottom-up approach and a top-down approach. The bottom-up approach involved developing an emissions inventory that counted all activity from traffic, burning and other sources. What we see is that the largest sources of nitrogen are cars, trucks and boats. We also found that major sources of hydrocarbons in the basin are from the mobile sources as well as natural sources such as trees.In the top-down approach, we conducted source-receptor modeling to establish where particulates were coming from. We wanted to determine the significance of road dust and emissions from wood burning and mobile sources.